Apparatus for balancing propeller blades



Jan. 21, 1 $QU|RES APPARATUS FOR BALANCING PROPELLER BLADES Filed July 5, i953 E. /f/ WW o L l INVENTOR Jbrz rpzfz'res.

9/ ATTORNEYS.

Patented Jan. 21, 1936 UNITE-o 'sTAr Esy APPARATUS FOR BALANCING PROPELLER BLADES' John Squires, Hagerstown, AMd.l Application July 5, 1933, Serial No. 679,135l

9 claims. (c1. 'z3-51)v This invention relates to improved apparatus for balancing propeller blades which may, if desired, be employed in the practice of the method set forth in my United States Letters Patent No. 1,968,540, and particularly propeller blades vof the type adapted for use in connection with viate unbalanced conditions in propellers 'of the type used 'on airplanes; to provide animp'roved balance testing apparatus for this purpose by the use of which corrections to` be individually made in each blade of the propeller may be de-v termined; to provide apparatus of this kind for determining what` corrections are necessary for rendering identical the characteristics'of propeller blades with reference to a corresponding reference plane of each so that one or more: 'l blades of a propeller may be removed and replaced Without requiring the assembled propeller to be rebalanced.

Other objects of the invention are provide an improved balance testing apparatus for proi pellerblades; to provide apparatus of this character which is adapted to delintely indicate, in selected units, the degree that a propeller blade is unbalanced with respect to a predetennined standard of balance; to provide means in ap#- paratus of. .this kind for accurately measuring the out of balance of a propeller blade in units which can conveniently be converted'to linear units that designate the 'change in the position of the center of mass of the blade required to bring the latter into perfect balance with apredetermined standard of balance; and to provide a blade holding member in, a balance` testing apparatus of the kind ,described for supporting a propeller lblade in a manner similar to that in which it is normally held by the hub of the'propeller.

. The. above being among the objects of the present invention, the same consists of certain novel features of construction andcombinations of parts to be hereinafter describedwith reference to the accompanying drawing, and then claimed, having the above and other objects in view.

In the accompanying drawing which illustrates a suitable embodiment of the present invention and in 'which' like numerals referto like parts throughout the .several different views,

y Fig. 1- is a front elevational `view of a propeller-of the airplane type equipped with removable propeller blades which the present 'invention generally relates to, a portion of the hub being broken away to illustrate the manner of secur- Fig." 2 is an enlarged partially sectioned side elevational view of one of the propeller blades shown mounted in the propeller in Fig. 1.

"Fig, 3 is an enlarged transverse sectimal'view` taken on line 3-3 of Fig. 2.

Fig. 4 is a side elevational view of my improved propeller blade balance' testing apparatus with a blade of the character shown in the lpreceding figures" mounted therein.

Fig'. 5 is an enlarged side e1evauona1 view or `the apparatus shown in Fig. 4, av 'portion only of the propeller blade being Shown.

Fig. 6 is an end view of the apparatus shown in Fig. 5, and taken from the right hand en d rthereof as viewed in Fig. 5.

the blad as determinedv by the apparatus illus-f trated in-Figs. 4 to 8, inclusive.

-The high speeds at which propellers of the type used on airplanes arerrotated demand that the blades of the propeller be balanced within close limit. 'I'hus the moment created bythe mass of each blade with respect tothe axis of rotationof the propeller must be substantially equal. Where-a propeller is provided with replaceable blades, it is extremely desirable ,that one blade may be removed from' the propeller and replaced by another like blad'e without disturbing the balanced :condition of the propeller. In order that removal of one blade of a propellerl and subsequent replacement by another will not materially affect the balanced condition of the propeller as a whole, it will of course be obvious that the moment ofthe new blade with respect to the axis o! rotation of the Ipropeller must be substantially identical to that o f the blade which vided forin the production of the blades whereby each blade of a certain size and type will confil 'ment between any -such blade being tested and the predetermined moment desired so indicated ,as to enable such variations as may be necessary to be made in the blade to bring itsl moment into conformance with the predetermined standard.

Referring to the drawing, it will be noted that Fig. 1 illustrates a propeller including a hub structure indicated generally as at'50 and oppositely extending blades |00. In the present case each of the blades |00 4is provided at its inner or root end with a peripheral flange |06 which is received within a complementary groove formed interiorly of the hub 50. Although, in the broader aspects of the present invention; the particular mode of securing the blades |00 to the hub 50 is more or less immaterial as long as the blades' are provided with a radial ange or equivalent means which serves to locate them 'radially with respect to the axis of rotation of the propeller, for the purpose of illustration the flange |06' and its manner of engagement with the hub 50 is assumed in the present instance to be substantially the same as is indicated in my Letters Patent of the United States No. 1,897,536, for improvements in Propeller, issued February 14, 1933. In the present instance the flange |06 serves as the sole means of supporting the corresponding blade |00 in the hub 50 and is provided with anl outer or tip face |96 lying in a plane perpendicular to the longitudinal axis of the blade |06 and an inner or root end face |98 of frusta-conical formation.' The main body portion of the blade ls of course of the usual airfoil section as illustrated in Fig. 3 having a lleading edge |06, a trailing edge H6, a front or camber face H00, and a rear or flat face |0b. 'Ihe grooves of the propeller hub 50 in which the flanges |06 of the blade |00 are received are accurately machined and they are accurately located at equal distances from the axis of rotation of the propeller hub.

The moment created by a blade is a function of its mass and the distance of its center of mass from the axis of rotation of the propeller and therefore changes in the moment of a blade may be produced by shifting it outwardly With respect to the axis of rotation of the propeller. In the present instance the moment arm, or distance between the axis of rotation of the propeller and the center Vof mass of the blade is varied by trimming 01T the inner and/or4 outer face of the ange |06 which is received in the groove of the propeller hub by an amount necessary toV bring it to accordance with a flxed standard. Only the side faces |96 and |98 of the flange |06 of each blade is engaged by the walls of its groove and thus either the inner or outer side faces of the `flange may be relied upon to determine the 'location of the center of mass of each blade which it is to be received so as to permit correct'ions to be made in the location of the center of mass of the blade with respect to the flange, and the outer side face E36 of the ange |06 initially usually occurs in too close proximity to the center of mass to allow the blade as originally formed to balance the standard moment differential of the testing apparatus. As the blank from which the blade is formed is machined accurately both internally and externally, as specifically brought out in my co-pending application for Letters Patent of the United States for improvements in Propeller blade and method of producing same, led July 5, 1933, and serially numbered 679,133 the distribution of Weight in all blades of the same size and type is substantially the Vsame and therefore only slight corrections in the location of the centers of mass of the blades are required.

s 'In Figs. 4 to 8, inclusive, is illustrated an apparatus for -equalizing the moments of the blades of a propeller with respect to the axis of rotation thereof. This apparatus includes a block 432 of substantial weight having a tapering dovetailed groove 434 centrally disposed at one end which extends between and is open at the respectivelyv opposite sides 436 and 438 of the block 432, for receiving the flange |06 of a propeller blade. The groove 434 is undercut in parallelism with the side edges thereof, as best shown in Fig. 5, the undercut portion being shaped in section complementary to the section of the flange |06 so as to removably receive the flange therein and thereby enable the blade to be secured relative to the block 432 without contact of the block with the shank of the blade.

Formed on the respectively opposite sides 436 and 438 of the block 432 are trunnions 440 and 442 which. rest upon the horizontal knife edge supports 444 and 446 respectively and pivotally support the block. The trunnions 440 and 442 are in alignment with each other bu't they are in misalignment with the center of mass of the block 432. They are located inA closer proximity tothe end of the block in which the flange receiving groove 434 is formed than to the opposite end of the block. This arrangement sets up a moment differential between the portions ofthe block on respectively opposite sides of the axis of the trunnions 440 and 442 which is of a predetermined amplitude. The trunnions are equidistant from the top and bottom of the block and their axis lies in the central plane passing through the center of the groove 434.

A graduated bar 448 is provided on one side of the block 432 substantially in the plane passing through the axis of the trunnions 440 and 442V and the horizontal center line-of the groove 434. The graduated bar 448 is offset slightly from the side of the block 432 by means of supports 44E arranged preferably at the ends of the graduated bar 448 so asto provide room for a weighted slide 4.50 which straddles the graduated bar 448 and may be moved 'longitudinally thereon. When movedtoward its extreme left hand position in Fig. 5 the Weighted slide 450 augments the moment dierential of the block 432. When a propeller blade is mounted in the groove of the block the weighted slide 450 may be moved to the right or to the left so as to balance the propeller blade supported by the block. The scale 45| on the bar 448 may be suitably arranged to conveniently indicate changes necessary in the ange of the propeller blade to bring the face of the ange |06.

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its moment to the desired standard. A convenient arrangementvis to graduate the scale in tenths of an inch and to provide a slidel 450 -having a weight equal'to 1/100th of the weight of the blade. Y With this ,arrangement each graduation on the scale will correspond to l/1000th of an inch variation in the location' of Thus when with the blade mounted in the balancing apparatus it is found that the Weighted slide 450 has to be moved one graduation on the scale in order to produce accurate balancing it indicates that '.the face of .the flange |06 must be trimmed 1/1000th of an inch -in order to produce the desired static moment in the blade.

The weightof the block 432 and the location of the trunnlons 440 and 442 thereon may be difficult to predetermine exactly and accurately. In order to aid in adjusting the moment differential and produce the condition which is desired for testing the blade, there may be pro. vided -means in the block 432 for adjusting its moment. This may conveniently -consist of a bolt 452 or the like thre'aded into a seat 453 in the end of the block 432 opposite the groo-ve The seat 463` preferably lies in the plane passing through the axis of the trunnions 4440 and 442 and the center line of the slot 434. It

ywill be perceived that the `-bolt 452 may be moved in o r out of its seat 453 to produce the correcting effect desired.

The description of the balancing apparatus so far relates to the use of the apparatus when the propeller is in a horizontal position and such use is important as has been indicated. Since the propeller, the adjustable bolt 452, the weight 450 and the bar 448- are all symmetrically arranged with respectto the axis of the trunnions 4,40 and 442, it is possible to turn the apparatus on the knife edges 444 and 446 yso that the propeller extends in a vertical direction as indicated in Fig. 8. Since the face of the flange |06 is at right angles to the axis of the propeller, the apparatus should remain at rest with the axial k,line of the blade' at the tip thereof directly un- 'der the axis of the trunnions 440 and-442, and

a trial of the balancing apparatus in the vertical position thus may be a convenient method of assuring that the center of gravity of the l mined thickness without changing the location of the tip end side\face |96 of the flange. If the -cut is required at the tip end side face |96 of `,the Jiange" |06 and is suflicient to reduce the thickness thereof to its predetermined thickness,

' then the root end side face |98 of the flange |06 is left unaltered, as indicated in Fig. l0, except perhaps to more accurately dimension the beveled'face |98. These two cases are not usual ones. Generally the tip end side face |96 is trimmed off sufliciently to' bring the blade into f flange |06 of predetermined thickness and shape to suit the hub with which it is to be used.

It is, of course entirely possible to employ the e 3 root end side face |98 of the flange 06 as lthe reference plane for determiningl the location of the center of mass of a blade from the axis of rotation of a propeller hub in whichv the blade is. to be mounted. Under these circumstances the root and side face |98 of the flange |06 is machinedrst during modification of the flange to bring the blade into balanced relationship with a stan iard momentdiierential, and then suicient metal is removed from the tip end side face |96 of the flange |06 to bring the flange to o and the centers are accurately located preferablyl on the longitudinal 'axis of lthe blade passing through its center of mass. With the blade thus supported, a suitable tool (not shown) f is employed to remove the required metal from the ange |06 to bring it tolinal shape, size and location. Preferably a grinding tool will be used as thus a more delicate adjustment may be procured. This method of-supporting the blade for nishing the flange insures that the plane of the flange |06 will be normal to a line passing cen- I trally through and axially of the flange, and also through the center of mass of the blade.

It will be apparent from the above that by the method disclosed herein it is possible to form any number of propeller blades so that their centers of mass will all'be located at such points that eachblade will have the same static moment about the center of rotation of the propeller of which they are tov form a part.

Formal changes may be made in the specic embodiment of the invention described without departing from the spirit and substance of the broad invention, the scope of which is commensurate with .the appended claims.

l. Apparatus for balancing propeller blades in.- cluding a pivotally mounted memberhaving `a standard moment differential `on one side of its pivotal axis, means on lsaid member forreceivling a ange of a propeller blade and detachably. supporting the latter on the other side of said pivotal axis with its longitudinal axis in aplane substantially normal to the pivotal axisofsaid member, including a reference surface engageable with one side of said flange for predetermining the distance of said side of said flange from said axis and including means for positively urging said ange into engagement with said reference surface, and means for varying the moment differential of the'respectively opposite sides of said member `by known increments so as to determine the amount the moment of said blade varies from `said standard moment,

said last mentioned means including a scale and a shiftable weight constructed, arranged and calibrated so asv to indicate in units of thickness, the correction required in the thickness'of said f flange to bring said blade to said predetermined standard.

2. Apparatus for balancing propeller blades including a weighty member, a pair of` co-axial trunnions, one on each side of said member located in misalignment with its center of mass, t

means coacting with thesaid trunnions for pivotally supporting said member, means at the end of said member which is closer to said trunnions, having a channel for receiving the flange of the propeller blade so as to detachably support the latter, said channel having a-side lwall adapted to predetermine the distance between a side of said iiange and the axis of said trunnions and having a relatively inclined wall for holding flanges of dierent thicknesses in engagement with said iirst mentioned wall, and mechanism at the other side of the trunnions from the means for supporting the blade for balancing said blade including graduated means for de- 'terrnining variations in the moment of said blades.

3. Apparatus for balancing propeller blades including a weighty member, a pair of co-axial trunnions, one on each side of said member locatedY in misalignment with its center of mass, means co-acting with said trunnions for pivotally supporting said member, means at the end of said member which is closer to said trunnions for receiving a ange of a propeller blade and detachably supporting the latter, said means including a pair of relatively inclined. opposed surfaces for positively positioning a reference surface on said flange at a predetermined distancefrom the axes of said trunnion, and mech.- anism at the other side of the trunnions Afrom the means for supporting the bladeA in a plane including the axes of said trunnions and the axis of the supported blade for balancing said blade including graduated means for determining variations in the moment of said blades.

4'. Apparatus for balancing propellerv lblades,Y

including a pair of supports, a lblock pivotally mounted on said supports having a larger portion of its mass on one side of its pivotal axis than on the other, means on the lighter end of said block for receiving a'peripheral flange of the hub end of a propeller blade and having. a reference surface engageable with one side of said ange and an element for urging blades of diiferent thicknesses into firm engagement with V`said reference surface. for predetermining the being provided with a tapering *dove-tailedgroove for receiving ailange of the hub end 'of a propeller blade so as to predetermine the'location of a side of said ange with respect to the pivotal axis of said block, and variable balancing mechanismonf said block for determining the difference in the vmoment of said blade and said standard moment differential and includ 'ing a scale calibrated to indicate the change in the thickness o! said ilange required to shift the center ofA mass of 'said blade sumciently to equalize the moment of said blade with the moment differential ofsaid block.

-6. Apparatus for balancingv propeller blades including a pivotally mounted block having a standard moment diierential about its pivotal axis, means on the end portion of said block of lower moment for'receiving al ange ofthe hub end of a propeller blade including a reference surface engageable with said fiangefor predetermining the location of va side of said flange from said axis and including means for urging 5 a surface of said flange into engagement with said reference surface, and variable balancing mechanism on said block fordetermining the difference in the moment of said blade and said standard moment diierential and including a scale having graduations thereon that are proportional lto linear units of thickness of, said flange for determining the change in the thick; ness of said ange required to shift the center of mass of said blade sufliciently to equalize the 15 moment of said blade'with said standard moment differential. y Y

7. Apparatus for lbalancing propeller blades including a pivotally mounted block having `a standard moment differential about its pivotal 20 axis, the end vportion of said block of lower moment being provided with a tapering dovetailed groove for receiving a vilange of the hub end of a propeller .blade so as to predetermine the location of said side of said ange with 25 respect to said axis, a scale on said block, aweight slidable von said scale in a direction parallel with-thesupported propeller blade and approximately equally *disposed on opposite sides of a lplane including the pivotalaxis of said 30 block andthe axis of said blade, said weight cooperating with said scale to. indicate the unbalance of said'blade with respect tosaid standard moment differential. y

8. Apparatus for balancing propeller blades ina5 cluding a pivotally mounted block having a standard moment diifere'ntial. about 'its pivotal axis,4 means on.the end portion of said block of lower moment for receiving va iiange of the hub end of a propeller blade,4 said means being so-40 constructed and arranged as to predetermine the location of a side of said flange .with respect to the pivotal axis of said block, a scale .on said block, a weight slidable on said scale in a direction parallel with the supported propeller' blade 4| vand approximately equally. disposed on opposite pendicular relationship tosaid pivotal axis and l including reference surfaces engageable fwith 60 arcuately spaced portions .of a side of said ilange for predetermining the location thereof with respect to said-axis, and variable' balancing mecha:- nism on said block 'for determining the difference in the moment of said blade and' said standard 65 moment-differential and including ascale calibrated.V tol indicate the change 'in the thickness of l'said flange required to shift the centervof mass of said blade sufficiently to equalize the moment of said blade with the moment difieren-'.70 tial oit-.said block. i Y 'y lJOHN SQUIRES. 

